Spark ignition apparatus



March 31, 1964 Y K. D. COLLINS 3,127,540

SPARK IGNITION APPARATUS Filed Jan. 22, 1962 A 2 Sheets-Sheet 1 March 31, 1964 Filed Jan. 22, 1962 K. D. COLLINS SPARK IGNITION APPARATUS 2 Sheets-Sheet 2 United States Patent 3,127,540 SPARK IGNITION APPARATUS Keith Douglas Collins, Watford, England, assignor to Rotax Limited, Willesilen, London, England Filed Jan. 22, 1962, Ser. No. 167,586 Claims priority, application Great Britain Jan. 31, 1961 10 Claims. (Cl. 315- 180) This invention relates to spark ignition apparatus of the kind comprising a transformer having a primary and a secondary Winding, means for supplying current intermittently to the primary winding from a source of direct or rectified alternating current, a capacitor connected across the secondary winding through a rectifier, and a control gap adapted to control the voltage at which the capacitor discharges through the spark gap.

With such apparatus the sparking voltage is determined by the voltage at which the control gap commences to .conduct. In certain applications it is found that under some conditions the required energy of the discharge must be considerably in excess of that normally required. Thus, for example on some aircraft a four joule discharge will suflice for must purposes, but when the ambient temperature is low or the aircraft is flying at a high altitude a twelve joule discharge may be required. It is detrimental tothe life of a spark plug defining the spark gap to pass discharge at a constant energy of twelve joules, and the object of the invention is to overcome this difiiculty in a convenient manner.

Spark ignition apparatus in accordance with the invention comprises in combination a pair of transformers having primary and secondary windings, switch means in circuit with the primary windings and movable between a first position in which one of the primary windings is energised, and a second position in which both primary windings are energised, means for breaking the circuits to the primary windings intermittently so as to generate a high voltage in the secondary windings, a pair of capacitors connected across the secondary windings through rectifiers respectively, a pair of control gaps each having two spaced electrodes connected across the pair of capacitors respectively so that the control gaps break down when the voltages across the capacitors reach a predetermined value, and a pair of conductive bands surrounding the control gaps respectively and connected to an electrode of the other control gap respectively, breakdown of one control gap applying a bias to the band surrounding the other control gap to reduce the breakdown voltage thereof.

In the accompanying drawings FIGURES 1 and 2 are circuit diagrams illustrating two examples of the invention respectively, and FIGURE 3 illustrates a modification of the example seen in FIGURE 1.

Referring first to FIGURE 1, there are provided first and second terminals 3, 4 adapted for connection to a source of direct or rectified alternating current so as to be of relatively positive and negative polarity in use, and first and second transformers 5, 5* having primary windings '6, 6 secondary windings 7, 7 and control windings 8, 8 respectively. One end of the winding 6 is connected to the collector of an n-p-n transistor 9, whilst the other end of the winding 6 is connected both to a terminal 10 of a switch 11 and also, through parallel paths containing respectively a resistor 12 and a capacitor 13, to the base of the transistor 9. One end of the winding 8 is connected through a resistor 14 to the base of the transistor 9, whilst its other end is connected to the emitter of the transistor 9 and to the terminal 4.

The transformer 5 has a similar set of components which are indicated by similar reference numerals with the suffix a. Moreover the switch 11 is movable from the position shown, in which it'connects both windings 6, 6

to the terminals 3, 4, to positions in which it connects the winding 6, 6 alternatively to the terminals 3, 4.

Each of the transformers 5, 5 when energised, acts in a similar manner to produce an output in the respective secondary winding 7, 7 as follows:

Considering the transformer 5, initially a small bias is applied to the base of the transistor 9 to permit a small current flow to the primary winding 6. The build-up of current in the winding 6 induces a voltage in the control winding 8 which biases the base of the transistor 9 further, to increase the flow of current to the primary winding 6. This regenerative action continues until the transistor becomes saturated, at which point the current in the primary winding 6 is constant, so that there is no feed back to the control winding 3. The bias on the base of the transistor 9 is thus removed and the transistor is cut on, the collapse of flux in the core of the transformer 5 inducing a high voltage in the secondary winding 7.

The ends of the secondary winding 7 are interconnected by a capacitor 15 in series with one or more rectifiers 16, the capacitor 15 being bridged by a resistor 17. Moreover, one end of the winding 7 is connected through the rectifiers 16 to one electrode 18 of a first control gap 19, the other electrode 20 of which is connected to a terminal 21. The other end of the winding 7 is connected to a terminal 22, the terminals 21, 22 being bridged by a spark gap 23 connected in parallel with a resistor 24.

The circuit associated with the winding '7 is similar to that associated with the Winding 7, and the components have been designated with similar reference numerals with the sufiix a. It will be noted, however, that the components 21, 22, 23, 24 are common to both circuits.

Surrounding the control gap 19 is a conductive band 25 which is connected to the electrodes 18 20 through a capacitor 26 and an inductor 27 respectively. A second conductive band 25 surrounds the control gap 19 and is connected to the electrodes 18, 20 through a capacitor 26 and an inductor 2'7 respectively.

In use, under normal conditions the switch 11 is set so that one or other of the transformers 5, '5 is energised. This transformer serves to charge the capacitor 15 or 15 connected across the secondary winding until the breakdown voltage of the respective control gap 19 or 19 is reached, when the capacitor 15 or 15 discharges through the spark gap 23.

Where a discharge of greater energy is required the switch is set so that both transfonmers 5, 5 are energised simultaneously. In this case both the capacitors 15, 15 are charged. As soon as one of these capacitors, say the capacitor 15, begins to discharge through the control gap 19 the capacitor 26 and inductor 27% form an oscillatory circuit and, since they are connected to the band 25 reduce the breakdown voltage of the ga 19 and thereby induce discharge of the capacitor 15 In this way it is ensured that the capacitors 15, 15 discharge substantially simultaneously, even if the charging rates of the capacitors 15, 15 are not exactly equal, so that a higher energy discharge is passed through the spark gap 23.

Referring now to the example illustrated in FIGURE 2, there are provided a pair of terminals 36, 37 which are adapted for connection to a source of direct or rectified alternating current so as to be of relatively negative and positive polarity in use respectively. There is further provided a pair of transformers 3 1, 31a having primary windings 32, 32 and secondary windings 33, 33 respectively.

One end of each winding 32, 32 is connected through inductors 38, 38 to terminals 39, 39* respectively. The other ends of the windings 32, 32 are connected through interrupters 34, 34* respectively and an inductor 35 to the terminal 36.

Moreover, the interrupters 34, 34 are bridged by capacitors 41, 41 respectively, and the terminals 36, 39, 39 are earthed respectively through capacitors 42, 43, 43

One end of the secondary winding 33 is connected through a rectifier 44, a resistor 45 and a rectifier as in series to one electrode 47 of a control gap 4%, the rectifiers 44, as and resistor 45 being bridged by a resistor 54.

Moreover, the other end of the winding 33 is connected through a capacitor 4h to the electrodes 47. The other electrode 55 of the gap is connected to a terminal 50 which is connected to a terminal 51 through a resistor 52. The terminals 5t 51 are adapted for the connection therebetween of a spark gap 53, and moreover the terminal Sll, which is earthed, is connected to said other end of the winding 33.

A similar set of components are associated with the winding 33 the corresponding components being indicated by the same reference numerals with the suffix a.

The spark gaps 53, 55 are mounted in close proximity.

Moreover, the control gaps 43, 48* includes surrounding bands 56, 56 respectively, the bands ss, 56 being connected tothe electrodesSS, 55 respectively. Furthermore, the electrodes 47, 47a are interconnected through a resistor 57.

In operation, depending on the posit-ion of the switch 40 one or both of the transformers 31, 31a is energised, the interrupters 34, 34 being opened periodically at intervals in synchronism to cause a high volt-age to be induced in one or both secondary circuits. One or both of the capacitors 49, 49 is thus charged until the corresponding control gap breaks down. The connections between the bands 56, 56a and the electrodes 55*, 55 ensure that when both transformers are operating the gaps 48, 48* break down substantially simultaneously even if the capacitors 49, 4 9 do not charge at exactly equal rates,

' since breakdown of one gap causes a voltage to be applied to the band of the other gap to reduce its breakdown voltage. The resistor 57 serves to maintain the voltage the two secondary circuits substantially equal when both are operating.

It will be appreciated from the foregoing examples that the particular form of the primary circuit is unimportant. Moreover, in both examples either one or two spark gaps could be employed.

FIGURE 3 illustrates in part a modification of the example shown in FIGURE -1, and like parts have been designated with the same reference numerals. In the example two spark gaps 23, 23 and associated resistors 24-, 24 are provided. Moreover, the control gaps 19, 19* are provided withiadditional conductive bands '71, 71 respectively which are connected to the electrodes 20 2%. The operation of the circuit is similar to thatin FIGURE 1, the additional bands serving to implement the action of the bands 25, 25 7 Although apparatus in accordance with the invention is primarily intended for use in aircraft, it may also be used in other applications such, for example, as road vehicles and industrial furnaces.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. Spark ignition apparatus comprising in combination a pair of transformers having primary and secondary windings, switch means in circuit with the primary windings and movable between a first position in which one of the primary windingsis energised, and a second position in which both primary windings are energised, means for breaking the circuits to the primary windings intermittently so as to generate a high voltage in the secondary windings, a pair of capacitors connected across the secondary gaps respectively.

rounding the control gaps respectively and connected to ergy passing through the control gaps, said return path including at least one spark gap.

2. Spark ignition apparatus as claimed in claim 1 and including a pair of inductors through which said bands are connected to said one electrodes of the other gaps respectively, and a. pair of capacitors through which said bands are connected to the otherelectrodes of said other 3. Spark ignition apparatus as claimed in claim 2 and including a second pair of conductive bands surrounding the control gaps respectively and connected to said one electrode of the other control gaps respectively.

4. Spark ignition apparatus as claimed in claim 1 in which one plate of each of said pair of capacitors is studied, the apparatus further including a resistor connected between the other plates of the capacitors.

5. Spark ignition apparatus as claimed in claim land including a pair of spark gaps mounted in close proximity and through which said pair of capacitors discharge respectively when the control gaps break down.

6. Spark ignition apparatus as claimed in claim 1 and including a single spark gap through which said pair of capacitors discharge when the control gaps break down.

7. Spark ignition apparatus as claimed in claim 1 in which said means for breaking the circuit to the primary windings intermittently comprises a pair of transistors. 8. Spark ignition apparatus as claimed in claim 1 in which said means for breaking the circuit to the primary windings intermittently comprises a pair of interrupters.

9. Spark ignition apparatus comprising in combination first and second transformers having primary and secondary windings, switch means in circuit with the primary windings and movable between a first position in which one of the primary windings is energised, and a second position in which'both primary windings are energised,

-means forbreaking the circuits to the primary windings intermittently so as to generate a high voltage in the first a pair of inductors connecting the second electrodes of the first and second control gaps to the bands surrounding the second and first control gaps respectively, third and fourth capacitors connecting the first electrodes of the first and second control gaps to the bands surrounding the second and first control gaps respectively, and a spark gap having ioiie'e'lectrode connected to the second electrodes of the control gaps, and its other electrodes connected to said other ends of the secondary windings, the arrangement being that breakdown of one control gap applies abias to the band surrounding the other control gap to reduce the breakdown voltage thereof.

l0. Spark ignition apparatus comprising in combination first and second transformers having primary and secondary windings, switch means in circuit with the primary windings and movable between a first position in which one of the primary windings is energised, and a second position in which both primary windings areenergised, means for breaking the circuits to the primary windings intermittently so as to generate a high voltage in the first and second secondary windings, first and second control gaps each having a first electrode, a second electrode and a surrounding conductive band, rectifiers through which the first electrodes of the first and second control gaps are connected to one end of the first and second secondary windings respectively, first and second capacitors through which said first electrodes are connected to the other ends of the first and second secondary windings respectively, means connecting the second electrodes of the first and second control gaps to the bands surrounding the second and first control gaps respectively, a pair of spark gaps interconnecting the second electrodes of the control gaps and said other ends of the secondary windings respectively, said other ends being earthed, and a resistor connected between the first electrodes of the control gaps, the arrangement being that breakdown of one control gap applies a bias to the band surrounding the other control gap to reduce the breakdown voltage thereof.

No references cited. 

1. SPARK IGNITION APPARATUS COMPRISING IN COMBINATION A PAIR OF TRANSFORMERS HAVING PRIMARY AND SECONDARY WINDINGS, SWITCH MEANS IN CIRCUIT WITH THE PRIMARY WINDINGS AND MOVABLE BETWEEN A FIRST POSITION IN WHICH ONE OF THE PRIMARY WINDINGS IS ENERGISED, AND A SECOND POSITION IN WHICH BOTH PRIMARY WINDINGS ARE ENERGISED, MEANS FOR BREAKING THE CIRCUITS TO THE PRIMARY WINDINGS INTERMITTENTLY SO AS TO GENERATE A HIGH VOLTAGE IN THE SECONDARY WINDINGS, A PAIR OF CAPACITORS CONNECTED ACROSS THE SECONDARY WINDINGS THROUGH RECTIFIERS RESPECTIVELY, A PAIR OF CONTROL GAPS EACH HAVING TWO SPACED ELECTRODES CONNECTED ACROSS THE PAIR OF CAPACITORS RESPECTIVELY SO THAT THE CONTROL GAPS BREAK DOWN WHEN THE VOLTAGES ACROSS THE CAPACITORS REACH A PREDETERMINED VALUE, A PAIR OF CONDUCTIVE BANDS SURROUNDING THE CONTROL GAPS RESPECTIVELY AND CONNECTED TO AN ELECTRODE OF THE OTHER CONTROL GAP RESPECTIVELY, BREAKDOWN OF ONE CONTROL GAP APPLYING A BIAS TO THE BAND SURROUNDING THE OTHER CONTROL GAP TO REDUCE THE BREAKDOWN VOLTAGE THEREOF, AND A RETURN PATH FOR ELECTRICAL ENERGY PASSING THROUGH THE CONTROL GAPS, SAID RETURN PATH INCLUDING AT LEAST ONE SPARK GAP. 